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          <h1 class="post-title" itemprop="name headline">【第三章】Vue全家桶+SSR+Koa2全栈开发美团网</h1>
        

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        <p>本文为《Vue全家桶+SSR+Koa2全栈开发美团网》的学习笔记的第三章，主要内容为Koa2基础知识<br>视频地址：<a href="https://coding.imooc.com/class/280.html" target="_blank" rel="noopener">https://coding.imooc.com/class/280.html</a></p>
<p>Koa官网：<a href="https://koa.bootcss.com/" target="_blank" rel="noopener">https://koa.bootcss.com/</a></p>
<a id="more"></a>

<h1 id="使用Koa-generator搭建环境"><a href="#使用Koa-generator搭建环境" class="headerlink" title="使用Koa-generator搭建环境"></a>使用Koa-generator搭建环境</h1><ol>
<li>安装Koa-generator脚手架<figure class="highlight cmake"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 注意： koa-generator需要全局安装</span></span><br><span class="line">npm <span class="keyword">install</span> -g koa-generator</span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><img src="/blog/images/20190910155454123.jpg" alt="安装Koa-generator脚手架"></p>
<ol start="2">
<li>创建koa2项目<figure class="highlight nginx"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># -e指定使用ejs模板引擎</span></span><br><span class="line"><span class="attribute">koa2</span> -e koa2-learning(项目名)</span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><strong>注意：如下图本人在创建koa2-learning项目时，使用的命令是”koa -e koa2-learning(项目名)”，这是错误的命令，<br>因为使用koa命令创建koa 1.x项目；使用koa2命令创建koa 2.x项目，所有应该按照上述命令输入</strong></p>
<p><img src="/blog/images/20190910155658373.jpg" alt="创建koa2项目"></p>
<ol start="3">
<li>安装项目依赖<br>按照上一步的提示，完成项目依赖的安装<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 安装项目依赖</span></span><br><span class="line"><span class="built_in">cd</span> koa2-learning</span><br><span class="line">npm install</span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><img src="/blog/images/20190910155933414.jpg" alt="安装项目依赖"></p>
<ol start="4">
<li>启动项目<br>按照第二步的提示，完成项目依赖的安装后启动项目<figure class="highlight routeros"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 启动项目</span></span><br><span class="line"><span class="builtin-name">SET</span> <span class="attribute">DEBUG</span>=koa2-learning:* &amp; npm start</span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><img src="/blog/images/20190910160410549.jpg" alt="启动项目"></p>
<p>在浏览器中输入<a href="http://localhost:3000/" target="_blank" rel="noopener">http://localhost:3000/</a> 即可访问这个项目：<br><img src="/blog/images/20190910160446726.jpg" alt="浏览器打开"></p>
<ol start="5">
<li>热加载方式启动项目<figure class="highlight dockerfile"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">npm <span class="keyword">run</span><span class="bash"> dev</span></span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><img src="/blog/images/20190910160856209.jpg" alt="热加载方式启动项目"></p>
<h1 id="ES7中的async和await语法"><a href="#ES7中的async和await语法" class="headerlink" title="ES7中的async和await语法"></a>ES7中的async和await语法</h1><blockquote>
<p>基于ES7开发了koa2</p>
</blockquote>
<h2 id="ES7中的异步"><a href="#ES7中的异步" class="headerlink" title="ES7中的异步"></a>ES7中的异步</h2><p>异步场景： 如何调用一分钟之后才出现的结果？  ———— 回调函数、异步</p>
<h2 id="ES7中的async和await"><a href="#ES7中的async和await" class="headerlink" title="ES7中的async和await"></a>ES7中的async和await</h2><blockquote>
<p>async 表示这是一个async函数，await只能用在这个函数里面。<br>await 表示在这里等待promise或者等待async函数中的promise返回结果了，再继续执行。<br>Promise 对象代表一个异步操作，有三种状态：Pending（进行中）、Resolved（已完成，又称 Fulfilled）和 Rejected（已失败）。Promise 对象的状态改变，只有两种可能：用 resolve 方法将 Promise 对象的状态，从「未完成」变为「成功」（即从 pending 变为 resolved）和用 reject 方法将 Promise 对象的状态，从「未完成」变为「失败」（即从 pending 变为 rejected）。</p>
</blockquote>
<p><strong><em>async声明的函数为异步函数，函数中可有await也可无await<br>如果函数体中有await，则函数必须声明为async</em></strong></p>
<ol>
<li><p>使用await将异步写法改为同步写法：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//1. await后面跟的是Promise对象</span></span><br><span class="line"><span class="comment">//2. 当有多个await时，会从上到下依次执行：即在前一个await没有执行完之前，后面的都不执行</span></span><br><span class="line"><span class="keyword">const</span> a = <span class="keyword">await</span> <span class="built_in">Promise</span>对象</span><br><span class="line"><span class="keyword">const</span> b = <span class="keyword">await</span> <span class="built_in">Promise</span>对象</span><br><span class="line"><span class="keyword">const</span> c = <span class="keyword">await</span> <span class="built_in">Promise</span>对象</span><br></pre></td></tr></table></figure>
</li>
<li><p>异步代码实例：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//index.js</span></span><br><span class="line">router.get(<span class="string">'/testAsync'</span>,<span class="keyword">async</span> (ctx) =&gt; &#123;</span><br><span class="line">	global.console.log(<span class="string">'start'</span>,<span class="keyword">new</span> <span class="built_in">Date</span>().getTime())</span><br><span class="line">	<span class="keyword">const</span> a = <span class="keyword">await</span> <span class="keyword">new</span> <span class="built_in">Promise</span>(<span class="function">(<span class="params">resolve,reject</span>)=&gt;</span>&#123;</span><br><span class="line">		setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">			global.console.log(<span class="string">'async a'</span>,<span class="keyword">new</span> <span class="built_in">Date</span>().getTime())</span><br><span class="line">			resolve(<span class="string">'ab'</span>)</span><br><span class="line">		&#125;,<span class="number">1000</span>);</span><br><span class="line">	&#125;)</span><br><span class="line">	<span class="keyword">const</span> b = <span class="keyword">await</span> <span class="number">12</span>;</span><br><span class="line">	<span class="keyword">const</span> c = <span class="keyword">await</span> <span class="keyword">new</span> <span class="built_in">Promise</span>(<span class="function">(<span class="params">resolve,reject</span>)=&gt;</span>&#123;</span><br><span class="line">		setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">			global.console.log(<span class="string">'async a'</span>,<span class="keyword">new</span> <span class="built_in">Date</span>().getTime())</span><br><span class="line">			resolve(<span class="string">'abc'</span>)</span><br><span class="line">		&#125;,<span class="number">2000</span>);</span><br><span class="line">	&#125;)</span><br><span class="line">	ctx.body=&#123;</span><br><span class="line">		a,</span><br><span class="line">		b,</span><br><span class="line">		c</span><br><span class="line">	&#125;</span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><strong><em>页面也是在三秒后才显示出来，数据也正常显示</em></strong><br><img src="/blog/images/20190912150409841.jpg" alt="异步代码实例"></p>
<ol start="3">
<li>同步代码实例(区别只是是否写了await)：<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line">router.get(<span class="string">'/testAsync'</span>,<span class="keyword">async</span> (ctx) =&gt; &#123;</span><br><span class="line">	global.console.log(<span class="string">'start'</span>,<span class="keyword">new</span> <span class="built_in">Date</span>().getTime())</span><br><span class="line">	<span class="keyword">const</span> a = <span class="keyword">new</span> <span class="built_in">Promise</span>(<span class="function">(<span class="params">resolve,reject</span>)=&gt;</span>&#123;</span><br><span class="line">		setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">			global.console.log(<span class="string">'async a'</span>,<span class="keyword">new</span> <span class="built_in">Date</span>().getTime())</span><br><span class="line">			resolve(<span class="string">'ab'</span>)</span><br><span class="line">		&#125;,<span class="number">1000</span>);</span><br><span class="line">	&#125;)</span><br><span class="line">	<span class="keyword">const</span> b = <span class="number">12</span>;</span><br><span class="line">	<span class="keyword">const</span> c = <span class="keyword">new</span> <span class="built_in">Promise</span>(<span class="function">(<span class="params">resolve,reject</span>)=&gt;</span>&#123;</span><br><span class="line">		setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">			global.console.log(<span class="string">'async c'</span>,<span class="keyword">new</span> <span class="built_in">Date</span>().getTime())</span><br><span class="line">			resolve(<span class="string">'abc'</span>)</span><br><span class="line">		&#125;,<span class="number">2000</span>);</span><br><span class="line">	&#125;)</span><br><span class="line">	ctx.body=&#123;</span><br><span class="line">		a,</span><br><span class="line">		b,</span><br><span class="line">		c</span><br><span class="line">	&#125;</span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><strong><em>页面马上显示出来，但数据未正常显示出来</em></strong><br><img src="/blog/images/20190912150621951.jpg" alt="同步代码实例"></p>
<h1 id="Koa2的中间件"><a href="#Koa2的中间件" class="headerlink" title="Koa2的中间件"></a>Koa2的中间件</h1><p>本小节内容摘录自：<a href="https://www.jianshu.com/p/9838ee0501e4" target="_blank" rel="noopener">https://www.jianshu.com/p/9838ee0501e4</a></p>
<h2 id="Koa2中间件的原理"><a href="#Koa2中间件的原理" class="headerlink" title="Koa2中间件的原理"></a>Koa2中间件的原理</h2><blockquote>
<p>Koa2的执行流程：好比水分进出洋葱一样，洋葱的每层相当于一个中间件，水分输入相当于请求Request，水分输出相当于相应Response。整个过程中，执行指针需要遍历两次中间件（除了最后一个中间件）。</p>
</blockquote>
<p><img src="/blog/images/20190910175020093.jpg" alt="Koa2的执行流程"></p>
<h2 id="自定义Koa2中间件"><a href="#自定义Koa2中间件" class="headerlink" title="自定义Koa2中间件"></a>自定义Koa2中间件</h2><ol>
<li><p>定义中间件</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//定义中间件基本格式</span></span><br><span class="line"><span class="comment">//1. 定义中间件</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">pv</span>(<span class="params">ctx</span>)</span>&#123;</span><br><span class="line">	<span class="comment">//ctx是应用中的全局对象：挂载所有的Request和Response，被各个中间件所引用</span></span><br><span class="line">	<span class="comment">//更多ctx的内容请见官网： https://koa.bootcss.com/#context</span></span><br><span class="line">	global.console.log(<span class="string">'pv'</span>,ctx.path)</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">//2.导出为一个异步函数</span></span><br><span class="line"><span class="built_in">module</span>.exports = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">	<span class="keyword">return</span> <span class="keyword">async</span> <span class="function"><span class="keyword">function</span>(<span class="params">ctx,next</span>)</span>&#123;</span><br><span class="line">		pv(ctx)</span><br><span class="line">		<span class="comment">//当前中间件运行暂停，将处理的控制权转交给下一个中间件</span></span><br><span class="line">		<span class="comment">//等待下个中间件运行结束，才运行当前中间件的后续代码</span></span><br><span class="line">		<span class="keyword">await</span> next()</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p>注册中间件到应用中</p>
<figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//使用app.use()注册中间件。每次客户端的请求，koa都会调用这个中间件。</span></span><br><span class="line"><span class="comment">//app.js</span></span><br><span class="line"><span class="keyword">const</span> pv = <span class="keyword">require</span>(<span class="string">'./middleware/koa-pv'</span>)</span><br><span class="line"></span><br><span class="line">app.<span class="keyword">use</span>(pv())</span><br></pre></td></tr></table></figure>
</li>
<li><p>中间件执行效果<br><img src="/blog/images/20190912152416865.jpg" alt="中间件执行效果"></p>
</li>
</ol>
<h2 id="中间件基本执行流程-栈式"><a href="#中间件基本执行流程-栈式" class="headerlink" title="中间件基本执行流程(栈式)"></a>中间件基本执行流程(栈式)</h2><p><img src="/blog/images/11524092-1e22309345e36284.webp" alt="中间件基本执行流程"></p>
<p><strong><em>中间件的引入是没有顺序的，但执行是有顺序的，而这个顺序通过洋葱的层的顺序来保证</em></strong></p>
<ol>
<li>代码示例如下：<figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//创建三个中间件，并注册到应用中</span></span><br><span class="line"><span class="comment">//1. 定义中间件</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">pv</span><span class="params">(ctx)</span></span>&#123;</span><br><span class="line">	<span class="comment">//ctx是应用中的全局对象：挂载所有的Request和Response，被各个中间件所引用</span></span><br><span class="line">	<span class="keyword">global</span>.console.log(<span class="string">'pv'</span>,ctx.path)</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">//2.导出为一个异步函数</span></span><br><span class="line">module.exports = <span class="function"><span class="keyword">function</span><span class="params">()</span></span>&#123;</span><br><span class="line">	<span class="keyword">return</span> async <span class="function"><span class="keyword">function</span><span class="params">(ctx,next)</span></span>&#123;</span><br><span class="line">		<span class="keyword">global</span>.console.log(<span class="string">'pv start'</span>)</span><br><span class="line">		pv(ctx)</span><br><span class="line">		<span class="comment">//当前中间件运行完毕，将处理的控制权转交给下一个中间件</span></span><br><span class="line">		await next()</span><br><span class="line">		<span class="keyword">global</span>.console.log(<span class="string">'pv end'</span>)</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">app.<span class="keyword">use</span>(pv())</span><br><span class="line">app.<span class="keyword">use</span>(m2())</span><br><span class="line">app.<span class="keyword">use</span>(m3())</span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><img src="/blog/images/20190912154429990.jpg" alt="中间件执行流程"></p>
<ol start="2">
<li>如果在中间件中没有编写await next()，则无法进入到下一个中间件，如下图所示：</li>
</ol>
<p><img src="/blog/images/20190912155034188.jpg" alt="中间件中没有编写await next()"></p>
<h1 id="Koa2的路由"><a href="#Koa2的路由" class="headerlink" title="Koa2的路由"></a>Koa2的路由</h1><h2 id="路由的写法"><a href="#路由的写法" class="headerlink" title="路由的写法"></a>路由的写法</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//index.js</span></span><br><span class="line"><span class="comment">//定义路由</span></span><br><span class="line"><span class="keyword">const</span> router = <span class="built_in">require</span>(<span class="string">'koa-router'</span>)()</span><br><span class="line"></span><br><span class="line">router.get(<span class="string">'/'</span>, <span class="keyword">async</span> (ctx, next) =&gt; &#123;</span><br><span class="line">  <span class="keyword">await</span> ctx.render(<span class="string">'index'</span>, &#123;</span><br><span class="line">    title: <span class="string">'Hello Koa 2!'</span></span><br><span class="line">  &#125;)</span><br><span class="line">&#125;)</span><br><span class="line"><span class="comment">//导出路由</span></span><br><span class="line"><span class="built_in">module</span>.exports = router</span><br><span class="line"></span><br><span class="line"><span class="comment">//app.js</span></span><br><span class="line"><span class="keyword">const</span> index = <span class="built_in">require</span>(<span class="string">'./routes/index'</span>)</span><br><span class="line">app.use(index.routes(), index.allowedMethods())</span><br></pre></td></tr></table></figure>

<h2 id="路由的三种返回类型"><a href="#路由的三种返回类型" class="headerlink" title="路由的三种返回类型"></a>路由的三种返回类型</h2><ol>
<li><p>返回页面</p>
<figure class="highlight dart"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">router.<span class="keyword">get</span>(<span class="string">'/'</span>, <span class="keyword">async</span> (ctx, next) =&gt; &#123;</span><br><span class="line">  <span class="keyword">await</span> ctx.render(<span class="string">'index'</span>, &#123;</span><br><span class="line">    title: <span class="string">'Hello Koa 2!'</span></span><br><span class="line">  &#125;)</span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure>
</li>
<li><p>返回字符串</p>
<figure class="highlight dart"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">router.<span class="keyword">get</span>(<span class="string">'/string'</span>, <span class="keyword">async</span> (ctx, next) =&gt; &#123;</span><br><span class="line">  ctx.body = <span class="string">'koa2 string'</span></span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><img src="/blog/images/20190912160022649.jpg" alt="返回字符串"></p>
<ol start="3">
<li>返回JSON<figure class="highlight dart"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">router.<span class="keyword">get</span>(<span class="string">'/json'</span>, <span class="keyword">async</span> (ctx, next) =&gt; &#123;</span><br><span class="line">  ctx.body = &#123;</span><br><span class="line">    title: <span class="string">'koa2 json'</span></span><br><span class="line">  &#125;</span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure>

</li>
</ol>
<p><img src="/blog/images/20190912160212417.jpg" alt="返回JSON"></p>
<h1 id="koa2操作cookie"><a href="#koa2操作cookie" class="headerlink" title="koa2操作cookie"></a>koa2操作cookie</h1><p>详见官网：<a href="https://koa.bootcss.com/#context" target="_blank" rel="noopener">https://koa.bootcss.com/#context</a></p>
<figure class="highlight stylus"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//通过 options 获取 cookie name:</span></span><br><span class="line">ctx<span class="selector-class">.cookies</span><span class="selector-class">.get</span>(name, [options])</span><br><span class="line"></span><br><span class="line"><span class="comment">//通过 options 设置 cookie name 的 value :</span></span><br><span class="line">ctx<span class="selector-class">.cookies</span><span class="selector-class">.set</span>(name, value, [options])</span><br></pre></td></tr></table></figure>

<p>代码示例：</p>
<figure class="highlight dart"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//index.js</span></span><br><span class="line">router.<span class="keyword">get</span>(<span class="string">'/'</span>, <span class="keyword">async</span> (ctx, next) =&gt; &#123;</span><br><span class="line">  <span class="comment">//设置cookie</span></span><br><span class="line">  ctx.cookies.<span class="keyword">set</span>(<span class="string">'pvid'</span>,Math.random())</span><br><span class="line">  <span class="keyword">await</span> ctx.render(<span class="string">'index'</span>, &#123;</span><br><span class="line">    title: <span class="string">'Hello Koa 2!'</span></span><br><span class="line">  &#125;)</span><br><span class="line">&#125;)</span><br><span class="line"></span><br><span class="line">router.<span class="keyword">get</span>(<span class="string">'/json'</span>, <span class="keyword">async</span> (ctx, next) =&gt; &#123;</span><br><span class="line">  ctx.body = &#123;</span><br><span class="line">    title: <span class="string">'koa2 json'</span>,</span><br><span class="line">	<span class="comment">//读取cookie</span></span><br><span class="line">	cookie: ctx.cookies.<span class="keyword">get</span>(<span class="string">'pvid'</span>)</span><br><span class="line">  &#125;</span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure>

<p><img src="/blog/images/20190912161018348.jpg" alt="设置cookie与读取cookie"></p>
<h1 id="常见错误"><a href="#常见错误" class="headerlink" title="常见错误"></a>常见错误</h1><h2 id="app-use-requires-a-generator-function"><a href="#app-use-requires-a-generator-function" class="headerlink" title="app.use() requires a generator function"></a>app.use() requires a generator function</h2><p><img src="/blog/images/20190912143928322.jpg" alt="koa2报错"></p>
<p>错误原因： Koa2的版本为1.X，应该使用2.X<br><strong>因为本人在创建koa2-learning项目时，使用的命令是”koa -e koa2-learning(项目名)”————使用koa命令创建koa 1.x项目；使用koa2命令创建koa 2.x项目</strong></p>
<p>解决办法： 使用”koa2 -e koa2-learning”重新创建项目，注意：一定要使用koa2 xxx,而不是koa xxx</p>

      
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              <div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#使用Koa-generator搭建环境"><span class="nav-number">1.</span> <span class="nav-text">使用Koa-generator搭建环境</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#ES7中的async和await语法"><span class="nav-number">2.</span> <span class="nav-text">ES7中的async和await语法</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#ES7中的异步"><span class="nav-number">2.1.</span> <span class="nav-text">ES7中的异步</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#ES7中的async和await"><span class="nav-number">2.2.</span> <span class="nav-text">ES7中的async和await</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#Koa2的中间件"><span class="nav-number">3.</span> <span class="nav-text">Koa2的中间件</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#Koa2中间件的原理"><span class="nav-number">3.1.</span> <span class="nav-text">Koa2中间件的原理</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#自定义Koa2中间件"><span class="nav-number">3.2.</span> <span class="nav-text">自定义Koa2中间件</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#中间件基本执行流程-栈式"><span class="nav-number">3.3.</span> <span class="nav-text">中间件基本执行流程(栈式)</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#Koa2的路由"><span class="nav-number">4.</span> <span class="nav-text">Koa2的路由</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#路由的写法"><span class="nav-number">4.1.</span> <span class="nav-text">路由的写法</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#路由的三种返回类型"><span class="nav-number">4.2.</span> <span class="nav-text">路由的三种返回类型</span></a></li></ol></li><li class="nav-item nav-level-1"><a class="nav-link" href="#koa2操作cookie"><span class="nav-number">5.</span> <span class="nav-text">koa2操作cookie</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#常见错误"><span class="nav-number">6.</span> <span class="nav-text">常见错误</span></a><ol class="nav-child"><li class="nav-item nav-level-2"><a class="nav-link" href="#app-use-requires-a-generator-function"><span class="nav-number">6.1.</span> <span class="nav-text">app.use() requires a generator function</span></a></li></ol></li></ol></div>
            

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